Proanthocyanidin (OPC) is said to be one of the efficacious components of the French Paradox, since it is contained in wine as well (1995, Clin. Chim. Acta. 235, 207-219). An antioxidant action, a peripheral circulation improving action, a blood flow improving effect, a hepatic function improving effect (2004, Japan Food Science, 403, January Issue, 40-45), and a platelet aggregation suppressing effect (Officially Published Patent Gazette 2003-527418) are known as the medicinal benefits of proanthocyanidin. Development of a method for convenient qualitative and quantitative evaluation of OPC, which is such an active ingredient, is therefore desired.
Known methods for analyzing proanthocyanidin include reversed phase HPLC by high-performance liquid chromatography-mass spectrometry (LC-MS) (2003, Biosci. Biotechnol. Biochem., 67, (5), 1140-1142), and normal phase HPLC involving gradient elusion by LC-MS (2003, J. Agric. Food Chem., 51, 7513-7521). However, both of these methods require MS detectors, and none of them are said to be convenient. Furthermore, proanthocyanidin is present as very many stereoisomers, owing to the stereoisomerism of flavan-3-ols which are the constituents of proanthocyanidin. There are limits on the compounds available as standard substances. Thus, its quantitative analysis has been impossible, except for some known compounds. Besides, proanthocyanidin exists in the natural world in forms ranging from the monomer flavan-3-ol to a dimer, a trimer, and further to n-mers of a higher polymerization degree. The analysis by reversed phase HPLC has shown that peaks of flavan-3-ol (monomer), the dimer and the trimer overlap.
As described above, no convenient method has been existent for the qualitative and quantitative evaluation of OPC.